<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    function fn1() {
        console.log(1);
    }
    function fn2() {
        console.log(2);
    }
    fn1.call(fn2);// 1
    fn1.call.call(fn2);// 2
</script>
</html>